1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a transflective liquid crystal display (LCD) device that is used both in a transmissive mode and in a reflective mode.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device includes two substrates spaced apart and facing each other, and a liquid crystal material layer interposed between the two substrates. Each of the first and second substrates includes an electrode, whereby the electrodes of each of the first and second substrates face each other. When a voltage is applied to each of the electrodes, an electric field is induced between the electrodes. Accordingly, an alignment of the liquid crystal molecules of the liquid crystal material layer is changed by the varying intensity or direction of the induced electric field. Thus, the LCD device displays an image by varying transmittance of light through the liquid crystal material layer according to the arrangement of the liquid crystal molecules. However, since the liquid crystal display (LCD) device is not luminescent, an additional light source is required to display images.
The liquid crystal display device may be categorized into two different types depending upon the type of light source used; a transmissive type and a reflective type. In the transmissive type, a back light is positioned behind a liquid crystal panel, wherein light incident from the back light enters into the liquid crystal panel. Accordingly, an amount of light transmitted through the liquid crystal material layer is controlled by the alignment of the liquid crystal molecules. Thus, the substrates and the electrodes must be formed of transparent conductive materials. Since the transmissive liquid crystal display (LCD) device uses the back light as a light source, it can display bright images in dark surroundings. In addition, the light intensity of the back light must be increased since the amount of transmitted light is relatively small. Consequently, the transmissive liquid crystal display (LCD) device requires a relatively high power consumption due to the low light intensity of the back light.
In the reflective type LCD device, ambient sunlight or artificial light is used as a light source of the LCD device. The ambient light incident from the surroundings is reflected by a reflective plate of the LCD device according to the arrangement of the liquid crystal molecules. Since there is no back light, the reflective type LCD device has considerably lower power consumption than the transmissive type LCD device. However, the reflective type LCD device may not be suitable for use in places with low ambient light since an artificial light source would be required.
FIG. 1 is a cross-sectional view of a transflective LCD device according to the related art. In FIG. 1, transmissive electrodes 12 are formed along an inner surface of a first substrate 11 that includes a thin film transistor (not shown) electrically connected to each of the transmissive electrodes 12. Reflective electrodes 13 are formed on the transmissive electrodes 12, and each has a transmissive hole 13a exposing a portion of the transmissive electrode 12. A first polarizer 14 is arranged along an outer surface of the first substrate 11, thereby linearly polarizing incident light.
A second substrate 21 is spaced apart from and faces the first substrate 11, and a color filter layer 22 is formed on an inner surface of the second substrate 21. The color filter layer 22 is composed of three sub-color filters of red (R), green (G), and blue (B). Each of the sub-color filters correspond to each of the transmissive electrodes 12. A common electrode 23 is formed on the color filter layer 22, and is made of a conductive transparent material. A diffusing film 24 and a second polarizer 25 are subsequently arranged along an outer surface of the second substrate 21, wherein a transmission axis of the second polarizer 25 is perpendicular to a transmission axis of the first polarizer 14. A liquid crystal material layer 30 is disposed between the reflective electrodes 13 and the common electrode 23.
In FIG. 1, a back light unit 40 is disposed beneath the first polarizer 14, and is used as a light source during a transmissive mode of the transflective LCD device. The back light unit 40 includes a light guide panel 42, a lamp 41, a collimating sheet 43, and a diffusing sheet 44. The light guide panel 42 includes scattering patterns formed along a lower surface, thereby changing linear light of the lamp 41 into plane light.
In a transmissive mode, a first light “L1”generated from the back light unit 40 penetrates into the first polarizer 14 and through the first substrate 11. In addition, the first light “L1” passes through the portion of the transmissive electrode 12 that corresponds to the transmissive hole 13a and through the liquid crystal material layer 30. Then, the first light “L1” is transmitted through the common electrode 23, the color filter layer 22, the second substrate 21, the diffusing film 24, and the second polarizer 25.
In a reflective mode, a second light “L2”incident from ambient surroundings, such as sunlight or artificial light, passes through the second polarizer 25, the diffusing film 24, the second substrate 21, the color filter 22, the common electrode 23, and the liquid crystal material layer 30. Then, the second light “L2”is reflected by the reflective electrode 13 and is transmitted back through the liquid crystal material layer 30, the common electrode 23, the color filter 22, the second substrate 21, the diffusing film 24, and the second polarizer 25.
By comparison, the transflective LCD device has lower reflectance than the reflective LCD device because of the transmissive hole 13a formed in the reflective electrode 13. Specifically, in the reflective mode, light incident toward the transmissive hole 13a is transmitted to the back light unit 40 and is not reflected. In addition, the transflective LCD device has lower brightness than the transmissive LCD device in the transmissive mode since light incident toward the reflective electrode 13 from the back light unit 40 is reflected toward the back light unit 40.